This invention relates to air conditioning systems in general, and specifically to an improved desiccant installation for a condenser having an attached receiver.
Automotive air conditioning systems typically include either an accumulator canister or a receiver canister that serve as a refrigerant reservoir. An accumulator is located just before the compressor, and allows only (or substantially only) refrigerant vapor to be drawn off of the top before compression, with liquid settling at the bottom. Receiver canisters are located just after the condenser, and are intend to allow only (or substantially only) liquid refrigerant to be drawn off the bottom for the refrigerant expansion valve. A canister of either type also provides a convenient location for a container of desiccant material, usually a bag or pouch of mesh material, which absorbs water vapor from the liquid refrigerant reservoir. Either an accumulator or a receiver usually has ample room within it for the desiccant, and some kind of pre-existing piping arrangement within it from which the desiccant bag can be conveniently suspended. The desiccant works better if suspended within, rather than resting free on the bottom of the canister, and is also less subject to damage in the event that a bottom closure is later welded to the canister. A typical example of such an arrangement may be seen in U.S. Pat. No. 4,354,362, where an internal pipe provides a practical suspension post for a desiccant container.
A relatively recent trend is the attached or so-called xe2x80x9cintegralxe2x80x9d receiver, into which a reservoir canister is incorporated structurally onto, on into, the return header tank of a so-called cross flow condenser design. A cross flow or xe2x80x9cheaderedxe2x80x9d condenser typically has a main pass, within which gas condenses to liquid, and a sub cooling section, within which liquid refrigerant is further cooled. An example may be seen in U.S. Pat. No. 5,537,839. The reservoir runs along the side of the return tank, and two openings or short pipes near the base of the return tank connect the main pass condenser tubes to the reservoir canister. The two openings are separate or discrete, so that all condensed refrigerant entering the return tank from the main pass is forced to flow through the upper opening and into the reservoir canister, where it forms a rising or falling reserve liquid column (depending on conditions). From the reservoir canister, liquid refrigerant can flow into the discrete lower opening and into the sub cooling section, and ultimately to the expansion valve. Generally, and preferably, the reservoir canister or tank section is no more than an empty vessel, with any internal structure suitable for suspending a desiccant cylinder or pouch. One exception may be seen in U.S. Pat. No. 5,159,821. There, refrigerant is forced centrally up into the reservoir canister in a fountain like central pipe, which also provides a convenient suspension pole for the desiccant cylinder. However, this is an undesirably complex and expensive structure.
More typically, the desiccant would simply rest where gravity would take it anyway, on the inside of the base of the reservoir canister, and this is the situation disclosed in the above mentioned U.S. Pat. No. 5,537,839. This puts the desiccant container both in a position where it could be damaged by welding or brazing on a bottom closure, and in a position where it is axially coextensive with, and could clog or block, the discrete openings between the reservoir canister and the return manifold. The patent recognizes this issue by providing a separate bottom threaded plug for installing the desiccant container. There is also provided an additional internal cage like structure to confine the desiccant away from the openings. That same structure retains the desiccant so that it is in line with the openings, and therefore at least theoretically capable of blocking them. Furthermore, the cage like structure represents a potential threat to the structural integrity of the desiccant container, which is generally a cloth or plastic open mesh, especially when subjected to vibration and bouncing in operation. Both the threaded plug and the retention cage also require additional cost and manufacturing steps.
Yet a further improvement is set forth in U.S. Pat. No. 6,170,287, assigned to the assignee of the subject invention and including some, but not all, of the inventors named herein. This patent discloses a simple cylindrical reservoir canister alongside the return tank. The main pass empties into the return header, which then empties into the reservoir canister through a discrete inlet just above the separator. From the reservoir canister, the liquid refrigerant empties back into the return tank through an outlet and then into the sub cooler section. There is no inner structure within the reservoir canister beyond the smooth inner wall, and it is preferably enclosed at top and bottom by a simple cap that is brazed or welded in place, giving a simple and reliable seal. A cylindrical, open mesh container of desiccant material has a diameter that gives it a small radial clearance from the inner wall of the reservoir canister, and an axial length which, if it were allowed to rest on the bottom of the reservoir canister, would put it in line with both the inlet and outlet, and liable to block free flow through them.
This is prevented under the invention of the ""287 patent by a standoff structure that consists of a narrow, centrally located bottom post and an upper, disk shaped base. The post is longer than the height of the inlet above the bottom end cap of the reservoir canister, and the base has an outer diameter that makes a tight interference fit with the inner wall of the reservoir canister. Therefore, the standoff structure can be used to insert the desiccant into the reservoir canister before the bottom end cap is sealed in place. The desiccant can be inserted past and beyond the inlet and outlet openings, where it will remain, at least temporarily, until after the bottom cap is welded in place, safe from heat damage. In later operation, the interference fit will help prevent vibration and damage of the desiccant tube within the canister, and even if the desiccant should sink downwards, the desiccant itself will never rest on the bottom of the canister, or block the inlet and outlet, because of the dimensions of the post. Cut outs are provided in the edge of the disk to allow liquid refrigerant to freely flow up or down past the disk.
The one-piece standoff prevents the desiccant bag from blocking the communication ports and is made of a material that allows ultrasonic welding of the polyester bag containing the desiccant. As alluded to above, the interference fit between the standoff and the interior wall of the cylindrical canister keeps the bag away from the heat generated by brazing or welding the end cap to the end of the canister. It is important that this interference fit require a high insertion force and not be degraded to the extent that desiccant bag can move within the canister after the end caps are brazed or welded in place. Such undesirable movement of the desiccant bag results in a rattle. The material selected for the standoff must meet the temperature criteria for ultrasonic welding to the polyester bag for the desiccant bag while at the same time resisting degradation from the welding or brazing of the end cap to the canister. The material of the standoff must balance between the welding to the desiccant bag and the heat deflection from welding or brazing the end cap to close the canister. A poor weld of the canister bag to the standoff can result in the bag detaching from the standoff in assembly and degradation of the interference fit between the standoff and the canister from excessive heat can result in rattle of the desiccant bag within the canister.
An improved standoff for desiccant in a condenser reservoir of automotive air conditioning system is provided by the subject invention.
In accordance with the subject invention, a desiccant material container is inserted within the interior wall of a canister having an inlet and an outlet along with a standoff. Thereafter, a spur is inserted into the canister and along the standoff into a position supported on and extending radially from the standoff and into an interference fit with the interior wall of the canister.
The spur may be of a material different than the material of the standoff whereby the spur withstands a higher temperature than the standoff. Accordingly, the subject invention facilitates a maximum and secure bond between the standoff and the desiccant bag while at the same time the spur maintains the integrity of the interference fit between the standoff and the canister after welding or brazing of the end cap to the canister to minimize rattle after prolonged use. This can be accomplished while at the same time reducing the insertion force required to insert the standoff and desiccant bag into the canister. In other words, the interference fit need not be over tight to allow for degradation from the heat of securing the end cap to the canister.